This invention relates to the recovery of tungsten values from scrap cemented tungsten carbide. More particularly, it relates to an improved process for recovering tungsten from the oxidation product of a cemented tungsten carbide.
Recovery of tungsten values from scrap tungsten carbide has been a problem in the carbide industry for a number of years. Cemented carbide tools are made by consolidating extremely hard and fine metal carbide particles together with a suitable binder or cement. Typically, such tools contain tungsten carbide cemented with cobalt although additional carbides such as the carbides of titanium, vanadium, chromium or molybdenum may also be present.
Cobalt is the most widely used cementing material although other cementing materials such as iron, nickel, chromium or molybdenum may be employed. Since all of the materials used in the cemented carbides are extremely valuable it is desirable to reclaim the materials found therein.
Various processes have been used in the past with varying degrees of success. U.S. Pat. No. 3,953,194 to Hartline et al describes a process for the reclaiming cemented metal carbide material by subjecting the metal carbide material to catastrophic oxidation to produce a mixture of metal oxide and the oxide of the cement. The resulting oxide is reduced and finally carbonized.
Another process described in U.S. Pat. No. 3,887,680 to MacInnis, Vanderpool and Boyer wherein tungsten carbide containing an iron group metal such as cobalt is oxidized from a friable oxidation product. The oxidation product is then ground and treated by digesting it in an aqueous solution of alkali metal hydroxide under controlled conditions to recover tungsten values.
U.S. patent application Ser. No. 827,745 entitled Oxidation of Tungsten Carbide, filed Aug. 25, 1977, to Vanderpool et al relates to a process wherein cemented tungsten carbide pieces are heated to a red glow in an enriched atmosphere of oxygen to result in a self-sustaining reaction whereby the pieces continue to oxidize after removal of heat.
U.S. Pat. No. 3,256,058 to Burwell describes a process wherein tungsten is recovered from wolframite or scheelite by fusing the ore at a temperature in excess of 698.degree. C. with a fusion mixture containing sodium carbonate, sodium chloride and sodium nitrate in a specific proportion.
Oxidation of cemented tungsten carbide by heating an oxygen containing atmosphere has proven to be a beneficial process. The present invention is directed to an improvement of this process.